1. Field of the Invention
The present invention relates to the field of graphics display systems.
2. Prior Art
Various types of graphics display systems are well known in the prior art. Of particular interest to the present invention are graphics display systems usable for the display of graphics information presented in digital form. By way of example, sequential readings of some parameter may be taken in digital form, or in analog form and converted to digital form, typically over a period of time or with the variation of some other parameter, which information is then desired to be displayed in curve form as if the information had been recorded on a conventional strip chart. One type of prior art system commonly used for such purposes may be referred to as a bit mapped raster scan display system. For a black and white display there is a bit in memory corresponding to each pixel location on the display, with the information in memory being read out and displayed in synchronism with the raster scan. Thus in concept there is a one-to-one mapping between the memory and the display. If the display is to include gray shade capability or color capability also, additional planes of memory must be provided so that two or more bits of information are available for each pixel. Frequently such systems utilize bit map memories which are significantly larger than the area which can be displayed at any one time, with the portion of the memory displayable being controlled by the operator. In this manner the display may be allowed to pan (move horizontally) and scroll (move vertically) around the larger memory area.
Display systems of the foregoing type have the advantage that virtually anything within the resolution of the display system may be displayed, as every pixel of the display may be separately defined. They have certain disadvantages however, that make their use less than ideal in applications where the flexibility of being able to separately define each and every pixel on the screen is not required. Among such disadvantages, are that they require very large amounts of memory, particularly when gray shades or colors to be provided or when the memory is to be substantially larger than the high resolution display itself Also, because the memory is large, the time required to load or alter the image or images in memory is rather long, making such systems aggravatingly slow during certain operations.
Various types of data compaction techniques are known both for display and other purposes. By way of example, run time or run length encoding has been used for various purposes. In a particular display, one might define a solid shape on the display by toggling the display on when the raster crosses the left boundary and off again a length of time or high frequency count corresponding to the desired position of the right hand side of the defined shape. Other compaction techniques include the storage in memory of the left and right edge definitions of a solid shape, and toggling the display on when the left edge is crossed and off again when the right edge is crossed. Either of these techniques will allow the generation of a shape on the display much faster than a pure bit mapped system, as one is generally only working with the start and endpoints in one form or another and not each and every pixel therebetween. Such techniques have the disadvantage however, that the types of things that can be displayed using such techniques is highly limited. By way of example, in general run length encoding cannot be used in conventional raster scan systems to display the variation of one parameter with time or with another parameter in graph form, as the number of times of reoccurrence of the same value of y for varying time or other x coordinate parameter cannot in general be predetermined.
Conventional raster scan display systems, including TV receivers, utilize a horizontal raster scan wherein the display is defined by a plurality of horizontal lines, each defining the respective line of the overall image. Generally, a given image frame will be comprised of two successive interlaced fields, the first field being comprised of every other image line, and the second field being comprised of the remaining image lines of the frame physically positioned between the lines of the first field. Display systems have been built utilizing a vertical raster scan in certain limited special situations. Generally however, such systems are otherwise conventional, the vertical raster scan being used only as a consequence of rotating a conventional wider than tall display to achieve a display that is taller than it is wide.